The field of the present disclosure relates generally to treating porous articles and, more specifically, to preparing disposable core dies to form a ceramic article.
At least some known turbine components, such as blades, nozzles, and vanes, have complex geometries. For example, turbine blades and nozzles may have internal passages and/or voids defined therein that must be manufactured in accordance with accurate dimensions having tight tolerances. In such instances, investment casting is generally effective at manufacturing parts that require dimensional accuracy and precision.
When manufacturing turbine components as described herein, investment casting may involve forming a disposable core die (DCD) by any suitable method. A low-viscosity, silica-based ceramic slurry is typically poured or injected into the DCD, and the slurry is cured such that the cured ceramic slurry conforms to the internal shape of the DCD. The cured ceramic core is then fired to produce a solidified ceramic core, the core is positioned within a shell mold, and the turbine component is formed such that the core defines the internal passages and/or voids of the turbine component when the core is removed from the shell mold.
One method of forming a DCD is in a rapid prototyping process. Rapid prototyping involves forming an object, based on a digital model, by layering material with a 3D printing machine. While rapid prototyping is effective at creating dimensionally accurate objects, the process generally uses auxiliary material to support the object being built. For example, solid objects formed with a 3D printing machine may include a wax-like auxiliary substance on the outer surface of the object, and hollow objects may also include the wax-like auxiliary substance within internal cavities of the object. For hollow objects such as a DCD, the auxiliary material may block the passage of slurry therethrough resulting in a ceramic core having incomplete structures.
One method of removing the auxiliary material from the object is to heat the wax-like substance such that it melts and drips off the object. While this method is effective in removing auxiliary material from the outer surface of objects, heating the wax-like substance may not effectively remove all the auxiliary material from internal cavities of hollow objects, especially when the internal cavities have a small and intricate design and/or dead-end passages. Thermal removal may be combined with solvent cleaning to clear excess material from internal cavities of a hollow DCD. While solvent cleaning clears the internal cavities of auxiliary material, a solvent such as hexane generally dissolves at least a portion of the material that the DCD is constructed from. As such, open pores may be formed in the previously impermeable walls of the DCD, which may alter the shape of and result in surface roughness on the formed DCD core. Accordingly, when the ceramic slurry is injected into the DCD and solidified, the DCD core formed therefrom will fall outside of acceptable dimensional tolerances because the slurry conforms to the altered DCD shape.